The long-term goal of this project is to elucidate the mechanism(s) by which the invariant natural T (iNKT) cells function in health and disease. iNKT cells are important immunoregulatory innate lymphocytes. They mediate the adjuvant function of alpha-galactosylceramide (alphaGalCer), a CD1d-restricted glycolipid antigen with potent in vivo immunomodulatory activities against metastatic tumours, certain infections and several autoimmune diseases. The rapid and robust cytokine response of in vivo activated iNKT cells mediates their immunoregulatory function. Instructional processes during ontogeny determine the effector properties of lymphocytes. Our approach to understanding iNKT cell biology has been to elucidate the intercellular and intracellular ontogenetic signals that lead to the development and differentiation of functional iNKT cells. We and others have recently discovered that classical nuclear factor kappaB (NF-kappaB) signalling is essential for the maturation and function of iNKT cells but not for conventional T cell ontogeny. This function of NF-kappaB is largely dependent on NF-kappaB1 (cell autonomous), to a lesser extent on NF-kappaB2, and RelB (cell extrinsic) activities. Therefore, a thorough characterisation of signals that activate NF-kappaB and its consequences during iNKT cell development and differentiation are essential to our understanding of iNKT cell biology. Here, we will test the central hypothesis that NF-kappaB is a lineage-specific regulator, which processes and integrates diverse extracellular signals that precisely regulate the development and differentiation of functional iNKT cells. To test this central hypothesis, we will pursue the following three integrated yet independent specific aims: (a) define the mechanism(s) that couples TCR signals to NF-kappaB activation during iNKT cell ontogeny; (6) define the signals that induce apoptosis in iNKT cells during development; and (c) define the mechanism(s) by which NF-kappaB regulates functional differentiation of iNKT cells. Upon completion of this project, our expectation is to define the molecular mechanism(s) by which NF-kappaB regulates the ontogeny and differentiation of functional iNKT cells. These findings will significantly enhance our fundamental understanding of iNKT cell biology and will lead to deeper insights into the molecular mechanisms underlying cell fate specification as well as molecular and functional differentiation within the immune system. Additionally, this knowledge can lead to the development of therapeutics that either enhance (adjuvant effect, downregulate autoimmunity) or suppress (cerebral malaria, airway hypersensitivity) iNKT cell function.